Analysis Of Structural Mechanical Characteristics Of Jointless Turnout On Bridge Under Complex Load

With the development of China’s railroad industry,high-speed railways are popularized and perfected in our land.As one of the key technologies of high-speed railways,jointless turnouts have seen great development,and a series of challenges and problems have come along with it.At present,most of the high-speed railroads in China adopt ballastless track structure and set up elevated bridges to improve the overall operation performance,which brings convenience and also brings many technical problems.High-speed turnouts on bridges combine the technical difficulties of seamless lines and turnouts on bridges.The changes of different material properties,such as pier settlement and concrete shrinkage creep,will have a certain degree of influence on the structural characteristics of individual parts of the turnout-bridge system and the force transmission mechanism.As the track structure is laid in the open air,the change of climate condition will damage the turnout structure and lead to the frequent occurrence of diseases,so the influence of the spatial location of the turnout and the sunlight temperature on the mechanical properties of the turnout-bridge system cannot be ignored.Therefore,this paper establishes the calculation model of seamless turnout on bridge under the temperature field to analyze the structural mechanical properties of turnout-bridge system under different sunshine and temperature conditions.The effect of daylight temperature effect on the structure of seamless turnout on the bridge is analyzed in four typical seasons,and the effect of various settlement patterns on the mechanical properties of the track in the turnout area and the smoothness of the track under the temperature field is investigated.The main work of this paper is as follows.(1)To elaborate the basic theoretical principles of the insolation temperature field,introduce the heat exchange mechanism between the turnout-bridge system and its surroundings,analyze the variation of solar radiation with angle,weather and duration for the turnout area and derive the formula for calculating the total solar radiation.This year’s meteorological data of the study site is collected and integrated with statistics,and the three-dimensional solar radiation temperature field is established with theory to obtain the real-time temperature distribution of the track structure.(2)Under solar radiation,the vertical temperature difference out of the median section of the box girder varies greatly,while the lateral temperature difference at the top of the box girder is not large,and the temperature on the left side is slightly smaller than that on the right side due to the influence of the lateral wind,and the vertical temperature gradually decreases and then increases from top to bottom.The internal temperature of the girder bridge is low and does not change much,while the bottom temperature is higher than the internal one,and the temperature distribution of the overall structure is close to the "s" shape.The temperature load values of each country were analyzed and compared with the calculation results to determine the temperature load loading in the region where the beam ends are located.(3)Through the above-mentioned temperature field and combined with the transfer mechanism between the turnout-bridge system to establish the bridge seamless turnout finite element model,the selection of static and thermal analysis parameters in the modeling process and the subsequent analysis are explained.Subsequently,the above numerical analysis method is used to calculate the temperature force and displacement of the track in the turnout area,and to verify the correctness of the temperature field and the analytical model.(4)The mechanical properties of each part of the track structure in a seamless turnout in winter and summer weather extremes are analysed.The additional temperature forces and displacements of the basic rail,core rail and guard rail increase significantly in winter weather compared to summer weather as the weather conditions change for the seamless single-opening turnout on the bridge,with similar effects on the spacer iron and no change in the restrictor.The effect of sunlight temperature on the seamless turnouts on the bridge was significant,and comparing the different loading modes,the overall temperature loading method generally used by the finite elements and the horizontal and vertical temperature gradient loading compared to the results obtained from the temperature field loading,the overall trend was similar but there was a certain difference between the two.The results obtained by fitting the vertical temperature profile to the vertical temperature gradient loading are more similar to those obtained by temperature field loading.(5)The basic theory of shrinkage creep of concrete is explained,and the mechanical properties of the track structure in the turnout area and the smoothness of the track under the action of shrinkage creep of the bridge are analysed and studied.The mechanical properties of the track structure of the bridge turnout under various types of bridge abutment settlement conditions are also investigated and the effects on the unevenness are studied.Finally,the influence of temperature effect and settlement combination on the mechanical properties of the track structure of the turnout-bridge system is investigated.